1. Field of the invention
The invention belongs to the field of coke making technology and relates to a new process for the removal of carbon sulphides from coke oven gas and to a new catalyst and its application.
2. State of the art
Coke oven gas (synonym: coking gas) is obtained from dry distillation of hard coal in coke oven plants. As main constituents, the gas typically contains approx. 55%-wt hydrogen, 25%-wt methane, 10%-wt nitrogen, and 5%-wt. carbon monoxide. Due to this, coke oven gas is generally qualified as a synthesis gas for chemical reactions. Disadvantageous, however, are the contents of carbonyl sulphide and carbon disulphide, which must previously be removed as they act as catalyst poisons in subsequent reactions, for example. The consequence is that the catalysts must frequently be cleaned or even exchanged, which directly involves effort and cost and is also unwanted because of the turnaround of the plant.
One method to free coke oven gas from unwanted carbon sulphides is to subject the gas to a catalytic hydrogenation and to convert the sulphur compounds into hydrogen sulphide. Although this gas is also unwanted, it can be washed out easily by means of aqueous lye, for example, ammonia solution.
Related processes are already known according to prior art. German patent application DE 1545470 A1 (Pichler), for example, suggests to hydrogenate carbon sulphides over cobalt molybdenum, nickel molybdenum or nickel cobalt molybdenum catalysts to hydrogen sulphide, which is then to be separated. The reaction temperature in the examples is above 550° C.
The use of catalysts on a nickel, cobalt, molybdenum or palladium basis for the hydrodesulphurisation of coke oven gas can also be found in various older Japanese patent applications, as, for instance, JP 59 145288 A2 (Shinnittetsu) or JP 59 230092 A1 (Hitachi).
A similar process is also known from German patent application DE 2647690 A1 (Parsons), which proposes to hydrogenate sulphur-bearing carbon compounds over catalysts on the basis of cobalt, molybdenum, iron, chromium, vanadium, thorium, nickel, tungsten and/or uranium and to remove the hydrogen sulphide obtained in an extraction column by means of an alkali hydroxide solution. The sulphides of the above metals are proposed as concrete catalysts. A disadvantage involved is, however, that in this case as well the catalysts require a minimum temperature of 260° C. and the hydrogenation must preferably be carried out at significantly higher temperatures, partly even above 400° C. This is not desired especially for reasons of energy cost. In addition, such temperatures will change the composition of the gas, i.e. methanation will take place already.
Although prior-art processes serve to transform carbon sulphides to hydrogen sulphide at high yields and to thus convert coke oven gases into synthesis gases of sufficiently high quality, they all involve the substantial disadvantage that these processes must take place at very high temperatures of considerably more than 280° C., as otherwise no adequate conversion rates will be achieved.